When blood pressure increases:
a. norepinephrine secretion increases.
b. baroreceptors detect the change in the carotid arteries.
c. the cardioregulatory center decreases parasympathetic stimulation of the heart.
d. heart rate and stroke volume increase.

a. norepinephrine secretion increases.

Explanation:

Norepinephrine (NE), is an organic chemical in the catecholamine family that performs the role of neurotransmitter in the brain and in the body it functions as hormone. Norepinephrine affects the way the brain pays attention and responds to events, it can increase heart rate, trigger the release of glucose (sugar) into the blood , Increase blood flow to muscles.

Let consider a case of a fight-flight response scenario, where blood level increases, as such:

Norepinephrine will also increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, and focuses attention. In the rest of the body, it  will increases heart rate and blood pressure.